A geogrid is commonly used for reinforcement of soil retaining wall, slope and weak ground in the civil engineering works. The geogrid needs to have some properties such as resistance to installation damage, friction feature and shape stability in addition to high tensile strength, low tensile stain and low creep strain. The geogrid is classified into plastic geogrid and textile geogrid according to its material and producing method.
The plastic geogrid is produced by passing a polymer sheet, extruded through an extruder, between rollers to perforate holes at regular intervals and then elongating the polymer sheet by one or two axes (see GB 19890020843), or produced by making lateral strips and longitudinal strips, which are made by extrusion-elongating polymer resin in a strip shape, into a flat lattice shape and then adhering the strips with the use of laser or frictional heat (see GB 2266540). However, the plastic geogrid shows serious creep strain when a load is applied for a long time thereto due to its material characteristics, thereby possibly causing deterioration of structural stability.
The textile geogrid is produced by weaving a lattice-type fabric with the use of high-tenacity fibers and then coating the fabric with polyvinylchloride, bitumen, acryl, latex, rubber resin or the like. The textile geogrid shows excellent tensile strength and creep characteristics owing to the usage of high-tenacity fibers. However, the textile geogrid is likely to be damaged depending on the state of soil in construction, so installation resistance is deteriorated. In addition, the textile geogrid is also not economically desirable since the producing procedure is too complex.
Meanwhile, WO 99/28563 discloses a method for producing a geogrid in which longitudinal strips made of fiber-reinforced polymer strips and lateral strips made of thermoplastic polymer resin strips are adhered in a lattice shape. In this document, it is disclosed that the thermoplastic polymer resin is extruded and inserted to form and adhere the lateral strips and to the longitudinal strips while the longitudinal fiber-reinforced polymer strips are moving, and the fiber-reinforced polymer strips may be inserted to the lateral strips. However, if the fiber-reinforced polymer strips are adhered in such a way, the fibers existing in the polymer may be damaged to deteriorate their tensile properties, and perfect adhesion between the strips is substantially not realized since the longitudinal and lateral polymer strips are not all in a melted state. In addition, since the geogrid in the aforementioned document has a flat structure, the geogrid has inferior friction behavior and unsatisfactory shape stability against a vertical load.